This invention relates to a pneumatic control valve for actuating the forward motion and reverse motion of a pneumatically driven apparatus from a rest position, in which, the movement of a slide valve in one direction or the other establishes a connection between a compressed air supply and either a forward channel or reverse channel and connects the other of the two channels to a non-pressurized scavenging air line in which control valve the stream of air flowing through the valve is throttled in dependence upon the particular pressure level prevailing.
Pneumatic control valves of this type have long been known. They are present, in particular, in so-called direct control systems, i.e. systems in which the power stream delivered to the pneumatic unit is controlled (cf. German Utility Model 81 17 890). Pneumatic crabs or pneumatic shunting trolleys on single-rail suspension railways are, for example, operated in this way. In this case, the control valve is either directly flanged onto the unit, so that cable or rod operation must be present, or, alternatively, the control unit hangs on a support from the apparatus, so that it is within reach of the operator.
Irrespective of the particular installation position, which affects the design of the valve, the pneumatic control valve should be as small as possible in its overall dimensions which, on the one hand, ensure a minimal space requirement and, on the other hand, provides for ease of handling. However, equal importance is attributed to structural simplicity in valves of the type in question to eliminate the risk of breakdown as far as possible. Operational breakdown are particularly unwelcome in underground work on account of the difficulty of carrying out repairs.
Hitherto known pneumatic control valves incorporate two operating units, namely the air distribution system on the one hand, and the air volume control, i.e. maintenance of a predetermined pressure, on the other hand. In some constructions, the two units are arranged separately from one another and are interconnected by hoses. The additionally required hose makes for a certain vulnerability, in addition to which the hoses in general can give rise to troublesome side effects by which operation is adversely affected. Although pneumatic control valves which have no additional hoses are already known, they still incorporate both operating units, resulting in a correspondingly complicated structure.
Accordingly, an object of the present invention is to provide a pneumatic control valve of the type described at the beginning which is safe in operation and particularly simple in structure, i.e. contains very few moving parts.